Separator roll and method of producing same

ABSTRACT

A separator roll etc. capable of reducing meandering is provided. The separator roll includes a core and a battery separator wound around the core. The core has an axis hole along a central axis of the core. A value, obtained by dividing a difference between a diameter of the core and a diameter of the axis hole by a width of the core in a direction of the central axis, is not less than 0.3 and not more than 1.5.

This Nonprovisional application claims priority under 35 U.S.C. §119 onPatent Application No. 2015-093011 filed in Japan on Apr. 30, 2015, theentire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a separator roll obtained by winding abattery separator around a core, and to a method of producing theseparator roll.

BACKGROUND ART

A lithium-ion secondary battery includes therein a positive electrodeand a negative electrode which are separated by a porous separator. Inproduction of lithium ion secondary batteries, a separator roll is used.The separator roll is obtained by winding this separator around a corehaving a cylindrical shape.

Patent Literature 1 discloses a separator roll having a core whose outerdiameter is 5 inch or more. Patent Literature 2 discloses a separatorroll having a core whose outer diameter is 200 mm and whose internaldiameter of an axis-bearing section is 75 mm.

CITATION LIST Patent Literature [Patent Literature 1]

WO 2011/024849 (published on Mar. 3, 2011)

[Patent Literature 2]

Japanese Patent Application Publication Tokukai No. 2013-139340(published on Jul. 18, 2013)

SUMMARY OF INVENTION Technical Problem

In a case of producing an application product of a battery separator(e.g. lithium ion secondary battery), a battery separator is wound offfrom a core of a separator roll before the battery separator is used. Atthat time, it is preferable that the battery separator can be wound offstraightly to a predetermined position of the application product.However, there is a case where the battery separator meanders when woundoff from the core. Patent Literatures 1 and 2 do not consider thismeandering at all.

The present invention was made in view of the foregoing problem. Anobject of the present invention is to provide a separator roll capableof reducing meandering and a method of producing the separator roll.

Solution to Problem

In order to solve the foregoing problem, a separator roll of the presentinvention is a separator roll, including: a core; and a batteryseparator wound around the core, the core having an axis hole along acentral axis of the core, a value being not less than 0.3 and not morethan 1.5, the value being obtained by dividing, by a width of the corein a direction of the central axis, a difference between a diameter ofthe core and a diameter of the axis hole.

A separator roll of the present invention is a separator roll,including: a core; and a battery separator wound around the core, thecore having an axis hole along a central axis of the core, the corehaving a diameter of less than 125 mm, a diameter ratio, obtained bydividing the diameter of the core by a diameter of the axis hole, beingnot less than 1.25 and not more than 1.65.

A method of the present invention of producing a separator roll is amethod of producing a separator roll, the separator roll including acore and a battery separator wound around the core, the core having anaxis hole along a central axis of the core, a value being not less than0.3 and not more than 1.5, the value being obtained by dividing, by awidth of the core in a direction of the central axis, a differencebetween a diameter of the core and a diameter of the axis hole, themethod comprising the steps of: inserting a take-up roller into the axishole and fixing the core to the take-up roller; and winding the batteryseparator around the core while rotating the core along with the take-uproller.

A method of the present invention of producing a a separator roll is amethod of producing a separator roll, the separator roll including acore and a battery separator wound around the core, the core having anaxis hole along a central axis of the core, the core having a diameterof less than 125 mm, a diameter ratio, obtained by dividing the diameterof the core by a diameter of the axis hole, being not less than 1.25 andnot more than 1.65, the method comprising the steps of: inserting atake-up roller into the axis hole and fixing the core to the take-uproller; and winding the battery separator around the core while rotatingthe core along with the take-up roller.

A method of the present invention of producing a separator roll is amethod of producing a separator roll, the separator roll including acore and a battery separator wound around the core, the core having anaxis hole along a central axis of the core, the method comprising thesteps of: inserting a take-up roller into the axis hole and fixing thecore to the take-up roller; and winding the battery separator around thecore while rotating the core along with the take-up roller, a lengthrepresented by Formula [1] below being less than 1.00 mm.

(2nt+φo)tan(cos⁻¹((φi−x)/(w ² +φi ²)^(1/2))−cos⁻¹(φi/(w ² +φi²)^(1/2)))  [1]

where

n is the number of times by which the battery separator is wound aroundthe core,

t is an average thickness of the battery separator [μm],

φo is a diameter of the core [mm],

φi is a diameter of the axis hole [mm],

x is 0.2 mm, and

w is a width of the core in a direction of the central axis [mm].

Advantageous Effects of Invention

The present invention can reduce a meandering width as compared with aconventional separator roll. Furthermore, the present invention canproduce a separator roll whose meandering width is smaller than that ofa conventional separator roll.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view illustrating a cross sectional configurationof a lithium-ion secondary battery.

FIG. 2 is a schematic view illustrating details of the configuration ofthe lithium-ion secondary battery illustrated in FIG. 1.

FIG. 3 is a schematic view illustrating another configuration of thelithium-ion secondary battery illustrated in FIG. 1.

FIG. 4 is a schematic view illustrating a configuration of a slittingapparatus for slitting the separator.

FIG. 5 is a view illustrating a configuration of each of cutting devicesin the slitting apparatus illustrated in FIG. 4.

FIG. 6 is a view illustrating a configuration of a separator roll inaccordance with an embodiment of the present invention.

FIG. 7 is a side view illustrating a state where a take-up roller isinserted into an axis hole of a core of the separator roll illustratedin FIG. 6.

FIG. 8 is a side view illustrating a state of the separator rollobtained when a separator is wound around the core in the stateillustrated in FIG. 7.

FIG. 9 is a front view describing a method of calculating an outerdiameter of the separator roll illustrated in FIG. 6.

FIG. 10 is an enlarged view illustrating an adhesive tape and portionsnear the adhesive tape in the separator roll illustrated in FIG. 6.

DESCRIPTION OF EMBODIMENTS

[Basic Configuration]

As regards a battery separator, of the present invention, for whichweight per unit area is to be measured, the following description willdiscuss (i) a lithium-ion secondary battery, (ii) a separator, (iii) aheat-resistant separator, (iv) a method of producing the separator andthe heat-resistant separator, (v) a slitting apparatus, and (vi) acutting device, in this order, each of which is a basic component of thepresent invention.

(Lithium-Ion Secondary Battery)

A nonaqueous electrolyte secondary battery, typified by a lithium-ionsecondary battery, has a high energy density, and therefore is currentlyand widely used as (i) batteries for use in devices such as personalcomputers, mobile phones, and mobile information terminals, (ii) movingbodies such as automobiles and airplanes, and (iii) stationary batteriescontributing to stable power supply.

FIG. 1 is a schematic view illustrating a cross sectional configurationof a lithium-ion secondary battery 1. As illustrated in FIG. 1, thelithium-ion secondary battery 1 includes a cathode 11, a separator 12(battery separator), and an anode 13. Between the cathode 11 and theanode 13, an external device 2 is connected outside the lithium-ionsecondary battery 1. This causes (i) electrons to move in a direction Awhile the lithium-ion secondary battery 1 is being charged and (ii)electrons to move in a direction B while the lithium-ion secondarybattery 1 is being discharged.

(Separator)

The separator 12 is provided so as to be sandwiched between (i) thecathode 11 which is a positive electrode of the lithium-ion secondarybattery 1 and (ii) the anode 13 which is a negative electrode of thelithium-ion secondary battery 1. The separator 12 is a porous film whichcauses the cathode 11 and the anode 13 to be separated and allowslithium ions to move between the cathode 11 and the anode 13. Materialsof the separator 12 include polyolefin such as polyethylene orpolypropylene.

FIG. 2 is a schematic view illustrating details of the configuration ofthe lithium-ion secondary battery 1 illustrated in FIG. 1. (a) of FIG. 2illustrates a normal configuration. (b) of FIG. 2 illustrates a state inwhich a temperature of the lithium-ion secondary battery 1 has risen.(c) of FIG. 2 illustrates a state in which a temperature of thelithium-ion secondary battery 1 has sharply risen. As illustrated in (a)of FIG. 2, the separator 12 has many pores P. Normally, lithium ions 3can move back and forth in the lithium-ion secondary battery 1, throughthe pores P.

The temperature of the lithium-ion secondary battery 1 may rise due to,for example, excessive charging of the lithium-ion secondary battery 1or a high current caused by short-circuiting of the external device.This causes the separator 12 to be melt or soften, so that the pores Pare blocked as illustrated in (b) of FIG. 2. As a result, the separator12 shrinks. This causes the lithium ions 3 to stop movingback-and-forth, and ultimately causes the temperature of the lithium ionsecondary battery 1 to sop rising.

Note, however, that in a case where a temperature of the lithium-ionsecondary battery 1 sharply rises, the separator 12 suddenly shrinks. Inthis case, the separator 12 may be destroyed (see (c) of FIG. 2). Thiscauses the lithium ions 3 to leak out from the separator 12 which hasbeen destroyed. As a result, the lithium ions 3 will never stop movingback and forth. Consequently, the temperature continues to rise.

(Heat-Resistant Separator)

FIG. 3 is a schematic view illustrating another configuration of thelithium-ion secondary battery 1 illustrated in FIG. 1. (a) of FIG. 3illustrates a normal configuration, and (b) of FIG. 3 illustrates astate in which a temperature of the lithium-ion secondary battery 1 hassharply risen. As illustrated in (a) of FIG. 3, the separator 12 can bea heat-resistant separator including a porous film 5 and aheat-resistant layer 4. The heat-resistant layer 4 is stacked on asurface of the porous film 5 which surface is on a cathode 11 side. Notethat the heat-resistant layer 4 can be alternatively stacked (i) on asurface of the porous film 5 which surface is on an anode 13 side or(ii) on both surfaces of the porous film 5. Furthermore, theheat-resistant layer 4 has pores which are similar to the pores P.Normally, the lithium ions 3 move back and forth through the pores P andthe pores of the heat-resistant layer 4. Materials of the heat-resistantlayer 4 include wholly aromatic polyamide (aramid resin).

Even in a case where the porous film 5 melts or softens due to a sharprise in temperature of the lithium-ion secondary battery 1, the shape ofthe porous film 5 is maintained (see (b) of FIG. 3) because theheat-resistant layer 4 supports the porous film 5. This causes theporous film 5 to come off with melting or softening. Therefore, thepores P only blocks up. This causes the lithium ions 3 to stop movingback and forth, and ultimately causes the above-described excessivedischarging or excessive charging to stop. In this way, the separator 12is prevented from being destroyed.

(Production Steps of Separator and Heat-Resistant Separator)

How to produce the separator and the heat-resistant separator of thelithium-ion secondary battery 1 is not specifically limited. Theseparator and the heat-resistant separator can be produced by awell-known method. The following discussion assumes a case where theporous film 5 contains polyethylene as a main material. Note, however,that even in a case where the porous film 5 contains another material,the separator 12 (heat-resistant separator) can be produced by employinga similar production method.

Examples of such a similar production method encompass a method whichincludes the steps of forming a film by adding inorganic filler or aplasticizer to a thermoplastic resin, and then removing the inorganicfiller or the plasticizer by means of an appropriate solvent. Forexample, in a case where the porous film 5 is a polyolefin separatormade of a polyethylene resin containing ultrahigh molecular weightpolyethylene, it is possible to produce the porous film 5 by thefollowing method.

This method includes (1) a kneading step of obtaining a polyethyleneresin composition by kneading a ultrahigh molecular weight polyethylenewith (i) an inorganic filler (such as calcium carbonate or silica) or(ii) a plasticizer (such as low molecular weight polyolefin or fluidparaffin), (2) a rolling step of forming a film by means of thepolyethylene resin composition, (3) a removal step of removing theinorganic filler or the plasticizer from the film obtained in the step(2), and (4) a stretching step of obtaining the porous film 5 bystretching the film obtained in the step (3). The step (4) can bealternatively carried out between the steps (2) and (3).

In the removal step, many fine pores are formed in the film. The finepores of the film stretched in the stretching step serve as theabove-described pores P. The porous film 5 (separator 12 having noheat-resistant layer) is thus obtained. Note that the porous film 5 is apolyethylene microporous film having a prescribed thickness and aprescribed air permeability.

Note that, in the kneading step, (i) 100 parts by weight of theultrahigh molecular weight polyethylene, (ii) 5 parts by weight to 200parts by weight of a low-molecular weight polyolefin having aweight-average molecular weight of 10000 or less, and (iii) 100 parts byweight to 400 parts by weight of the inorganic filler can be kneaded.

Thereafter, in a coating step, the heat-resistant layer 4 is formed onthe porous film 5. For example, by applying, onto the porous film 5, anaramid/NMP (N-methylpyrrolidone) solution (coating solution), theheat-resistant layer 4 that is an aramid heat-resistant layer is formed.The heat-resistant layer 4 can be formed on a single surface or bothsurfaces of the porous film 5. Alternatively, the heat-resistant layer 4can be formed on the porous film 5, by applying, on the porous film 5, amixed solution containing a filler such as alumina or carboxymethylcellulose.

Note that, in the coating step, an adhesive layer can be formed on theporous film 5, by applying a vinylidene polyfluoride or dimethylacetoamide solution (coating solution) on the porous film 5 (applicationstep) and coagulating the vinylidene polyfluoride or dimethyl acetoamidesolution (coagulating step). The adhesive layer can be formed on asingle surface of the porous film 5 or on both surfaces of the porousfilm 5.

A method of coating the porous film 5 with a coating solution is notspecifically limited, provided that uniform wet coating can be carriedout by the method. The method can be a conventionally well-known methodsuch as a capillary coating method, a spin coating method, a slit diecoating method, a spray coating method, a dip coating method, a rollcoating method, a screen printing method, a flexo printing method, a barcoater method, a gravure coater method, or a die coater method. Theheat-resistant layer 4 has a thickness which can be controlled byadjusting a thickness of a coating wet film or a solid-contentconcentration in the coating solution.

It is possible to use a resin film, a metal belt, a drum or the like asa support with which the porous film 5 is fixed or conveyed in coating.

It is thus possible to produce the separator 12 (heat-resistantseparator) in which the heat-resistant layer 4 is stacked on the porousfilm 5. The separator thus produced is wound around a core having acylindrical shape. Note that a subject to be produced by the aboveproduction method is not limited to the heat resistant separator. Theabove production method does not necessarily include the coating step.In a case where no coating step is included in the method, the subjectto be produced is a separator having no heat-resistant layer.Alternatively, an adhesive separator having other functional layer (suchas later-described adhesive layer), instead of the heat-resistant layer,can be produced by a production method similar to that of theheat-resistant separator.

(Slitting Apparatus)

The heat resistant separator or the separator including no heatresistant layer (hereinafter, referred to as “separator”) preferably hasa width (hereinafter, referred to as “product width”) suitable forapplication products such as the lithium-ion secondary battery 1. Note,however, that the separator is produced so as to have a width that isequal to or larger than a product width, in view of an improvement inproductivity. After the separator is once produced, the separator isslit into a separator(s) having the product width.

Note that the “separator width” means a length of the separator in adirection substantially perpendicular to a lengthwise direction and athicknesswise direction of the separator. Hereinafter, a wide separator,which has not subjected to slitting, is referred to as an “originalsheet,” whereas particularly a separator which has been subjected toslitting is referred to as a “slit separator.” Note also that (i)“slitting” means to slit the separator in the lengthwise direction (flowdirection of the film during production; MD: Machine direction) and (ii)“cutting” means to slit the separator in a transverse direction (TD).Note that the transverse direction (TD) means a direction which issubstantially perpendicular to the lengthwise direction (MD) and thethicknesswise direction of the separator.

FIG. 4 is a schematic view illustrating a configuration of a slittingapparatus 6 for slitting the separator. (a) of FIG. 4 illustrates anentire configuration, and (b) of FIG. 4 illustrates arrangements beforeand after slitting the original sheet. As illustrated in (a) of FIG. 4,the slitting apparatus 6 includes a rotatably-supported cylindricalwind-off roller 61, rollers 62 to 69, and take-up rollers 70U and 70L.The slitting apparatus 6 further includes cutting devices 7 describedlater.

(Before Slitting)

In the slitting apparatus 6, a cylindrical core c around which theoriginal sheet is wrapped is fit on the wind-off roller 61. Asillustrated in (b) of FIG. 4, the original sheet is wound off from thecore c to a route U or L. The original sheet which has been thus woundoff is conveyed to the roller 68, via the rollers 63 through 67. In theconveying step, the original sheet is slit into a plurality of slitseparators. Note that the roller 67 is not necessarily provided. In sucha case, the original sheet is conveyed from the roller 66 to the roller68.

(After Slitting)

As illustrated in (b) of FIG. 4, some of the slit separators are woundaround respective cylindrical cores u (bobbins), which are fit on thetake-up roller 70U.

Meanwhile, the others of the plurality of slit separators are woundaround respective cylindrical cores l (bobbins), which are fit on thetake-up roller 70L. Note that (i) the slit separators each wound aroundin a roll manner and (ii) the respective cores u and l are, as a whole,referred to as a “roll”.

(Cutting Device)

FIG. 5 is a view illustrating a configuration of each of the cuttingdevices 7 in the slitting apparatus 6 as illustrated in (a) of FIG. 4.(a) of FIG. 5 is a side view of the cutting device 7, and (b) of FIG. 5is a front view of the cutting device 7. As illustrated in (a) and (b)of FIG. 5, each of the cutting devices 7 includes a holder 71 and ablade 72. The holder 71 is fixed to a housing or the like provided inthe slitting apparatus 6. The holder 71 holds the blade 72 such that theblade 72 and original sheet of the separator being conveyed have a fixedpositional relation. The blade 72 (i) has a finely sharpened edge and(ii) slits the original sheet of the separator by using the edge.

Embodiments Configuration of Separator Roll

FIG. 6 illustrates a configuration of a separator roll 10 in accordancewith an embodiment of the present invention. (a) of FIG. 6 is a frontview illustrating a state in which the separator 12 has not been woundoff from the core 8. (b) of FIG. 6 is a side view of (a) of FIG. 6. (c)of FIG. 6 is a front view illustrating a state where the separator 12has been wound off from the cure 8. (d) of FIG. 6 is a perspective viewillustrating a state where the size of the core 8 is being measured. Asillustrated in (a) and (b) of FIG. 6, the separator roll 10 includes thecore 8 around which the separator 12 is wound. Note that the separator12 has been obtained by slitting the original sheet as above.

(Core)

The core 8 includes an outer cylinder part 81, an inner cylinder part82, and ribs 83 (support members), and has the same function as that ofthe cores u and l. The core 8 has an axis hole H whose center is acentral axis CA of the core 8.

The outer cylinder part 81 is a cylindrical member having an outercircumferential surface 81 a around which the separator 12 is wound. Theinner cylinder part 82 is a cylindrical member which is provided insidethe outer cylinder part 81 so as to surround the axis hole H. The ribs83 are eight support members which are provided, at intervals, betweenthe outer cylinder part 81 and the inner cylinder part 82 so as tosupport them. The core 8 has through holes h each surrounded by theouter cylinder part 81, the inner cylinder part 82, and the ribs 83.

Materials of the core 8 include an ABS resin. Note, however, that thematerials of the core 8 of the present invention are not limited to theABS resin but can alternatively include resins such as a polyethyleneresin, a polypropylene resin, a polystyrene resin, and a vinyl chlorideresin. It is preferable that the materials of the core do not includemetal, paper, and a fluorine resin.

(Separator)

As illustrated in (c) of FIG. 6, there is provided, on an outer surfaceof the separator 12, a tape 120 which is a sign indicating an end partof a product. Such a tape is often employed as the sign indicating anend part of a product. Alternatively, a seal, a stamp, or a print can beemployed as the sign. A surface of the separator 12 on which surface thetape 120 is provided is not limited to an outer surface of the separator12. The tape can alternatively be provided on an inner surface of theseparator 12.

The separator 12 is made up of (i) an inner circumferential part 121located on a side closer to the core 8 than the tape 120 and (ii) anouter circumferential part 122 located on a side farther from the core 8than the tape 120. An end of the separator 12 is attached to the core 8by an adhesive tape 130 (fixing tape). Specifically, the end of theseparator 12 is fixed to the outer circumferential surface 81 a by theadhesive tape 130 having an adhesive agent. Alternatively, the end ofthe separator 12 can be fixed to the outer circumferential surface 81 aby directly applying an adhesive agent to the end of the separator 12 orby a clip.

Unevenness of the outer circumferential surface 81 a is transferred tothe separator 12. Note that the unevenness is more easily transferred tothe inner circumferential part 121 than to the outer circumferentialpart 122. Accordingly, in a case where the separator 12 is used as acomponent of a battery, the outer circumferential part 122 divided bythe tape 120 is used. The inner circumferential part 121 has a length of3 m. The inner circumferential part 121 of the present invention is notlimited to have 3 m.

(Method of Measuring Size of Core)

As illustrated in (d) of FIG. 6, a diameter of the outer circumferentialpart 81 is measured by causing jaws m of a slide caliper M to contactthe outer circumferential surface 81 a of the outer cylinder part 81. Adiameter of the axis hole H is measured by causing jaws n of the slidecaliper M to contact an inner circumferential surface 82 b of the innercylinder part 82. A length of the rib 83 in a radial direction of thecore 8 is measured by causing (i) one of the jaws n of the slide caliperM to contact an inner circumferential surface 81 b of the outer cylinderpart 81 and (ii) the other of the jaws n to contact an outercircumferential surface 82 a of the inner cylinder part 82.

(Inclination of Core Required when Separator is Wound Around the Core)

FIG. 7 is a side view illustrating a state where a take-up roller R isinserted into the axis hole H of the core 8 of the separator roll 10illustrated in FIG. 6. (a) of FIG. 7 illustrates a state where the core8 is fixed to the take-up roller R without being inclined. (b) of FIG. 7illustrates a state where the core 8 is not yet fixed to the take-uproller R. (c) of FIG. 7 illustrates a state where the core 8 is fixed,at a slant, to the take-up roller R. (d) and (e) of FIG. 7 illustratesizes and angles for calculating an angle of inclination of the core 8.Note, in FIG. 7, that, only the inner circumferential surface 82 b ofthe inner cylinder part 82 of the separator roll 10 and the take-uproller R are indicated by full lines, for clarity of the drawing.

The take-up roller R includes a surface-protruding mechanism. In themechanism, (i) the take-up roller R causes its surface to thrust towardsand press against the inner circumferential surface 82 b of the innercylinder part 82 of the core 8. This allows a certain frictional forceto be applied to the internal circumferential surface 82 b, andultimately causes a rotating force of the take-up roller R to beconveyed to the inner circumferential surface 82 b. The take-up roller Rhas the same function as the take-up rollers 70U and 70L. As illustratedin (a) of FIG. 7, the core 8 is fixed to the take-up roller R withoutbeing inclined while the surface-protruding mechanism is normallyoperating. The rotation of the take-up roller R causes the core 8 torotate, and ultimately causes the separator 12 to be wound around theouter circumferential surface 81 a of the outer cylinder part 81 of thecore 8.

As illustrated in (b) of FIG. 7, while the surface-protruding mechanismis not being effective, the core 8 drops vertically downward bygravitation. Note that a gap length x₁ is a maximum length of a gapbetween the inner circumferential surface 82 b and the take-up roller R.

As illustrated in (c) of FIG. 7, while the surface-protruding mechanismis not entirely effective but is partially effective, the core 8 can befixed, at a slant, to the take-up roller R. An inclination angle θ1refers to an angle by which the core 8 is inclined from the innercircumferential surface 82 b (broken line) illustrated in (b) of FIG. 7.The maximum length of the gap between the inner circumferential surface82 b and the take-up roller R is substantially equal to the gap lengthx₁ illustrated in (b) of FIG. 7. The gap length x₁ is set toapproximately 1 mm, in a case where the core 8 is attached to ordetached from the take-up roller R. Due to an error in mechanicalaccuracy of the surface-protruding mechanism, 0.2 mm out of the gaplength x₁ of 1 mm (0.2 mm corresponds to x (gap length constant) in theabove Formula [1]) contributes to the inclination of the core 8.

(Angle of Inclination of Core)

A triangle Tb illustrated in (d) of FIG. 7 is obtained by dividing arectangle by its diagonal line, which rectangle is obtained when thecore 8, illustrated in (b) of FIG. 7, is viewed from a side thereof. Asize and an angle of the triangle Tb can be expressed by Equations (1)and (2) below. An angle θ2 is an angle of a vertex of the triangle Tbwhich vertex is on a side where the inner circumferential surface 82 bcontacts the take-up roller R in (b) of FIG. 7.

s=(w ² +φi ²)^(1/2)  (1)

cos θ2=φi/s  (2)

Equation (3) is derived from Equations (1) and (2).

θ2=cos⁻¹(φi/(w ² +φi ²)^(1/2))  (3)

φi: diameter of inner circumferential surface 82 b (diameter of axishole H) [mm]w: width of core 8 in central axis direction

A triangle Tc illustrated in (e) of FIG. 7 is obtained by dividing arectangle by its diagonal line, which rectangle is obtained when thecore 8, illustrated in (c) of FIG. 7, is viewed from a side thereof. Asize and an angle of the triangle Tc can be expressed by Equation (4)below, similarly with Equation (3). An angle θ3 is an angle of a vertexof the triangle Tc which vertex is on a side where the innercircumferential surface 82 b contacts the take-up roller R and fromwhich vertex inclination of the core 8 starts.

θ3=cos⁻¹((φi−x)/(w ² +φi ²)^(1/2))  (4)

At that time, a relation between the inclination angle θ1 and the anglesθ2 and θ3 can be expressed by Equation (5) below.

θ1=θ3−θ2  (5)

By substituting Equations (3) and (4) for 02 and 83 in Equation (5),Equation (6) below can be derived.

θ1=cos⁻¹((φi−x)/(w ² +φi ²)^(1/2))−cos⁻¹(φi/(w ² +φi ²)^(1/2))   (6)

(Width of Meandering of Separator 12)

FIG. 8 is a side view illustrating a state of the separator roll 10obtained when the separator 12 is wound around the core 8 in the stateillustrated in (c) of FIG. 7. (a) of FIG. 8 illustrates a state wherethe diameter of the outer circumferential surface 81 a of the outercylinder part 81 of the core 8 is relatively small. (b) of FIG. 8illustrates a state where the diameter is relatively large. Asillustrated in (a) of FIG. 8, in a case where the separator 12 is woundaround the core 8 in the state illustrated in (c) of FIG. 7, theseparator 12 is inclined from a direction perpendicular to the centralaxis CA of the core 8. A position at which the separator 12 is wound offfrom the separator roll 10 in such a state varies within a range definedby a meandering width d. The meandering width d can be expressed byEquation (7) below.

d=(2nt+φo)tan θ1  (7)

n: number of winding of separator 12t: thickness of separator 12 [μm]φo: diameter of outer circumferential surface 81 a (diameter of core 8)[mm]

The number n of winding of the separator 12 can be expressed by Equation(8) below.

n=(φf−φo)/2t  (8)

φf: diameter of separator roll 10 [mm]

FIG. 9 is a front view describing a method of calculating the diameterφf of the separator roll 10 illustrated in (a) of FIG. 6. (a) of FIG. 9illustrates a state where the separator 12 having a length L is woundaround the core 8. (b) of FIG. 9 illustrates a state where the separator12, wound around the core 8, is cut in a radial direction of the core 8so as to be flattened out. (c) of FIG. 9 illustrates a state where theseparator 12, wound around the core 8, is flattened out without beingcut.

As illustrated in (b) of FIG. 9, in a case where the separator 12, woundaround the core 8, is cut in a radial direction of the core 8 so as tobe flattened out, the separator 12 is substantially a trapezoid whenviewed from a side thereof. A short side Po of the trapezoid can beexpressed as “πφo”, a long side Pf of the trapezoid can be expressed as“πφf”, and a height of the trapezoid can be expressed as “(φf−φo)/2”.Accordingly, an area of the trapezoid can be expressed as “π(φf+φo)(φf−φo)/4”.

As illustrated in (c) of FIG. 9, in a case where the separator 12, woundaround the core 8, is flattened out without being cut, the separator 12is substantially an extremely elongated rectangle when viewed from aside thereof. An area of the rectangle can be expressed as “dL”.

Since the area of the rectangle and the area of the trapezoid are equalto each other, Equation (9) below can be derived.

dL=π(φf+φo)(φf−φo)/4  (9)

Equation (10) below can be derived from Equation (9).

φf=(4dL/π+φo ²)^(1/2)  (10)

As is clear from Equation (7), the meandering width d becomes smaller asthe inclination angle θ1 becomes smaller. As is clear from (b) of FIG.8, the meandering width d becomes larger as the diameter φo becomeslarger. By substituting Equation (6) in Equation (7), Equation (11)below can be derived.

d−(2nt+φo)tan(cos⁻¹((φi−x)/(w ² +φi ²)^(1/2))−cos⁻¹(φi/(w ² +φi²)^(1/2)))  (11)

(Conditions for Reducing Meandering Width)

TABLE 1 Com. Com. Symbol Unit Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7Ex. 8 Ex. 1 Ex. 2 Com. Ex. 3 Diameter of core φo mm 152 102 123 95 100123 123 123 200 200 125 Diameter of axis φi mm 75 75 75 75 75 75 75 7575 75 75 hole of core Width of core w mm 65 85 65 65 60 65 65 65 60 5030 Gap length x mm 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 constantThickness of t μm 16 16 16 16 16 20 12 20 16 16 16 separator Length of Lm 2500 2500 2500 2500 2500 1500 1500 400 2500 2500 2500 separatorDiameter of φf mm 272 248 257 245 247 231 195 159 302 302 258 separatorroll Number of times n 3753 4552 4188 4683 4589 2698 3002 903 3173 31734156 of windings of separator Inclination angle θ1 0.18 0.13 0.18 0.180.19 0.18 0.18 0.18 0.19 0.23 0.38 of core Meandering width d mm 0.840.58 0.79 0.75 0.82 0.71 0.60 0.49 1.00 1.20 1.71 of separator Diameterratio φo/φi 2.03 1.36 1.64 1.27 1.33 1.64 1.64 1.64 2.67 2.67 1.67Diameter φo − φi mm 77 27 48 20 25 48 48 48 125 125 50 differenceDiameter (φo − φi)/w 1.2 0.3 0.7 0.3 0.4 0.7 0.7 0.7 2.1 2.5 1.7difference/width of core diameter of φf/φi 3.6 3.3 3.4 3.3 3.3 3.1 2.62.1 4.0 4.0 3.4 separator roll/ diameter of axis hole of core Ex. standsfor Example. Com. Ex. stands for Comparative Example.

Table 1 shows the result of calculation of the meandering width dexpressed by Equation (11) with respect to each of various separatorrolls 10.

The inventors of the present invention have sought conditions forrestraining the meandering width d expressed by Equation (11) withrespect to each of various separator rolls 10, and found that when thelater-described conditions are met, it is possible to remarkablyrestrain a width by which the separator 12 meanders (hereinafter“meandering width”).

[First Condition]

As shown in Table 1, Examples 1 through 8 meet a condition that a value((φo−φi)/w) obtained by dividing a diameter difference (φo−φi) by thewidth w of the core 8 is not less than 0.3 and not more than 1.5 (firstcondition). According to Examples 1 through 8, the meandering width dfalls within a range of less than 1.00 mm. As above, meeting of thefirst condition allows the meandering width d to be restrained, ascompared with conventional separator rolls (e.g. those in ComparativeExamples 1 through 3). The value ((φo−φi)/w) is preferably not less than0.3 and not more than 1.2. In this case, the meandering width d fallswithin a range of not more than 0.84 mm. The value ((φo−φi)/w) is morepreferably not less than 0.3 and not more than 0.7. In this case, themeandering width d is in a range of not more than 0.82 mm.

[Technical Significance of First Condition]

As the difference between the diameter φo and the diameter φi becomeslarger, the meandering width d becomes larger. As the core width becomessmaller, the meandering width d becomes larger. When the value((φo−φi)/w) is more than 1.5, a reduction in core width gives rise to agreater contribution to an increase in meandering width. This can causethe separator 12 to meander to such an extent that a separator rollincluding the separator 12 is not acceptable as a battery separator.When the value ((φo−φi)/w) is less than 0.3, meandering is not adverselyaffected but a wide core is forced to be supported by a small gap. Thisgives rise to a significant difficulty in handling the core. In a casewhere the separator roll 10 meets the first condition, such problems canbe solved.

[Second Condition]

Specifically, Examples 2 through 8 meet a condition that the diameter φois less than 125 mm and a diameter ratio (φo/φi) is not less than 1.25and not more than 1.65 (second condition). According to Examples 2through 8, the meandering width d falls within a range of less than 1.00mm. As above, meeting of the second condition allows the meanderingwidth d to be restrained, as compared with conventional separator rolls(e.g. those in Comparative Examples 1 through 3). The diameter ratio(φo/φi) is preferably not less than 1.27 and not more than 1.64. Whenthe diameter ratio (φo/φi) is in this range, the meandering width d isin a range of not more than 0.82 mm. Furthermore, the separator roll 10meeting both the first and second conditions is encompassed in thepresent invention.

[Technical Significance of Second Condition]

In a case where the diameter φo is not less than 125 mm, there is apossibility that the separator roll 10 is difficult to convey. In a casewhere the diameter ratio (φo/φi) is less than 1.25, the outer cylinderpart 81 and the inner cylinder part 82 come close to each other. Thiscauses a lateral area of the core 8 to be reduced. In such a case, thereis a possibility that, while conveying the separator roll 10, a part ofa conveyer, human's finger etc. will contact not only a side surface ofthe core 8 but also a side surface of the separator 12 wound around thecore 8. This can cause a reduction in quality of the separator roll 10.In a case where the diameter ratio (φo/φi) is more than 1.65, there is apossibility that the separator 12 meanders to such an extent that aseparator roll including the separator 12 is not acceptable as a batteryseparator. In a case where the separator roll 10 meets the secondcondition, these problems can be solved.

(Stability in Winding Up and Winding Off)

The separator 12 is taken up while the separator 12 is being tensionedso as to prevent occurrence of wrinkles. This requires a frictionalforce between the inner cylinder part 82 of the core 8 and the take-uproller R which frictional force matches the tension applied to theseparator 12. Moments acting on objects having respective concentricshapes are proportional to radii of the respective concentric shapes.Accordingly, in a case where a force (tension) applied to an outermostperiphery is constant, the moment becomes larger as the radius becomeslarger. Therefore, the frictional force between the inner cylinder part82 of the core 8 and the take-up roller R which frictional force matchesthe tension is proportional to a radius of the separator roll 10(hereinafter “roll radius”). In a case where the roll radius becomeslarger, it is necessary to heighten the effect of the surface-protrudingmechanism in order that the tension and the frictional force match eachother. This can cause (i) the core 8 to deform or deteriorate and (ii)malfunction of the surface-protruding mechanism because of an excessiveload on the surface-protruding mechanism.

Also in a case where the separator 12 is wound off from the separatorroll 10, it is necessary to generate a frictional force which matches atension for winding off the separator 12. Specifically, the frictionalforce is required to be larger as the roll radius is larger.

[Third Condition]

The inventors of the present invention have found that it is possible toreduce a load on the surface-protruding mechanism, by meeting (i) thefirst or second condition and (ii) a condition that a value (φf/φi),obtained by dividing the diameter φf of the separator roll 10 by thediameter φi, is not less than 2.3 and not more than 3.5. Note thatφf=(2nt+φo).

[Technical Significance of Third Condition]

As the diameter φf becomes larger, the tension and the frictional force,which should match each other at the center of the separator roll 10,become larger. As the diameter φi becomes smaller, the tension and thefrictional force, which should match each other at the center of theseparator roll 10, become larger. In a case where the value (φf/φi) ismore than 3.5, there is a possibility that it is impossible to stablytake up or wind off the battery separator. In a case where the value(φf/φi) is less than 2.3, the frictional force is not adverselyaffected, but the length of the separator which can be taken up becomesextremely short. This requires frequently switching the separator rolls10 during manufacturing of a battery (i.e., a battery using theseparator 12 wound off from the separator roll 10). In this regard, theseparator roll in Example 8 is not preferable as a separator roll for abattery separator. Note, however, that in a case where the separatorroll 10 meets the third condition, the above problems can be solved.Since this stabilizes taking up and winding off of the separator 12, itis possible to restrain the meandering width as compared withconventional separator rolls.

<Effects of the Present Embodiment>

The separator roll 10, which meets the above conditions for restrainingthe meandering width, allows the meandering width d to be restrained ascompared with conventional separator rolls. A device for correctingmeandering of a battery separator (EPC device; Edge Position Controldevice) can correct a meandering width of approximately 1 mm at maximum.As such, the meandering width of the separator roll 10 can be correctedby such an EPC device. Specifically, the meandering width d of theseparator roll 10 is preferably less than 1.00 mm, and more preferablynot more than 0.80 mm.

(Stability of Roll)

If the separator 12 is wound around the core 8 and the diameter of thecore 8 is less than 125 mm, then the number of windings of the separator12 becomes larger, as compared with a conventional core. In a case wherethe number of windings becomes larger the separator 12 is wound aroundthe core 8 firmly particularly at a portion closer to the core 8. Inview of the circumstances, in a case where the diameter of the core isless than 125 mm, winding offset (phenomenon in which winding of theseparator roll 10 is misaligned like a bamboo shoot due to lateralimpact) is less likely to occur. This can provide a separator rollresistant to lateral impact.

(Reformation of Curl of Separator)

In a case where the separator 12 is wound around the core 8 whosediameter is less than 125 mm, a curve (curvature) of an outercircumferential surface of the core 8 becomes tighter (larger) than thatof a conventional core. In a case where the separator 12 is a stackingmember made up of a front surface and a rear surface containingrespective different materials, there is a possibility that warpagecalled “curl” appears due to a difference, in physical property, betweenthe front surface and the rear surface. One of methods of reforming thecurl is to (i) apply a force to the separator 12 in a desirabledirection (normally in a direction opposite to a direction in whichwarpage appears due to the difference in physical property) and (ii) fixthe separator 12 so that a resin constituting the separator 12 isplastically deformed. In a case where the diameter of the core 8 is lessthan 125 mm, the curve of the separator 12 wound around the core 8 istight. Accordingly, in a case where the separator 12 is wound off fromthe core 8, it is possible to easily reform the curl so as to make thecurl small.

(Easiness in Conveyance)

As illustrated in FIG. 6, the core 8 of the separator roll 10 has theplurality of through holes h each of which is a gap surrounded by theouter cylinder part 81, the inner cylinder part 82, and the ribs 83. Ina case where each length, in a radial direction of the core 8, of theplurality of through holes h is not less than 5 mm, the separator roll10 can be easily conveyed. This is because the separator roll 10 can beeasily conveyed by inserting a part of a movable body (conveyer, human'sfinger etc.) into the gap(s).

(Weight Saving)

Since the core 8 is smaller in diameter than a conventional core, theseparator roll 10 is lighter in weight than a conventional separatorroll. Furthermore, since the core 8 is smaller in diameter, the core 8can achieve a strength similar to that of conventional one although thecore 8 has a thickness smaller than the conventional one. This allowsthe separator roll 10 to be further lighter in weight. Furthermore, aseparator can be employed as the separator 12, which separator (i)contains, for example, an inorganic compound with a specific gravity of2.0 g/cm² or more and (ii) is heavier in weight than a conventionalbattery separator.

(Absorption of Unevenness)

FIG. 10 is an enlarged view illustrating the adhesive tape 130 andportions near the adhesive tape 130 in the separator roll 10 illustratedin FIG. 6. As illustrated in FIG. 10, an end of the innercircumferential part 121 of the separator 12 is attached to the outercircumferential surface 81 a of the core 8, via the adhesive tape 130.Since the inner circumferential part 121 is wound around the core 8 soas to cover the adhesive tape 130, the inner circumferential part 121partially has unevenness.

As illustrated in FIGS. 2 and 3, the separator 12 has innumerable poresas the pores P. Consequently, the separator 12 can be supposed to becrushable, in a thickness direction, depending on a porosity, in a casewhere a force is applied to the separator 12 in the thickness direction.For example, assume that the separator 12 has a thickness of 13 μm and aporosity of 50%. On that assumption, the separator 12, wound around thecore 8, can reduce its thickness by approximately 50 μm per eight layersof the separator 12. Accordingly, as the separator 12, wound around thecore 8, is farther from the outer circumferential surface 81 a (as thenumber of windings of the inner circumferential part 121 increases),unevenness of the separator 12, caused by the adhesive tape 130, isabsorbed by a decrease in thickness of the separator 12, i.e., isreduced.

Specifically, in a case where the diameter of the core 8 is, forexample, 6 inches, the length of the inner circumferential part 121,wound around the core 8 eight times, is approximately 3.8 m. In a casewhere the diameter of the core 8 is 5 inches, the length of the innercircumferential part 121, wound around the core 8 eight times, isapproximately 3.2 m. As the core 8 becomes smaller in diameter, thenumber of windings of the inner circumferential part 121 can increase.As has been described, since the core 8 of the separator roll 10 issmaller in diameter than a conventional core, it is possible to increasethe number of windings of the inner circumferential part 121, ascompared with the conventional separator roll 10. Besides, theunevenness of the separator 12, caused by the adhesive tape 130, can bemore absorbed by a decrease in thickness of the separator 12 as comparedwith conventional separator rolls. It is therefore possible to use theadhesive tape 130 whose thickness is larger (e.g. thickness of not lessthan 20 μm and not more than 100 μm) than a conventional one.

(Method of Producing Separator Roll)

A method of producing the separator roll 10 is also encompassed withinthe scope of the present invention. The method includes the steps of (i)inserting a take-up roller R into an axis hole H and fixing the core 8to the take-up roller R as illustrated in FIG. 7 and (ii) winding theseparator 12 around the core 8 (cores u and l in FIG. 4) while rotatingthe core 8 along with the take-up roller R (take-up rollers 70U and 70Lin FIG. 4) as illustrated in FIG. 4.

Furthermore, in the method, by setting the parameters below so that thevalue of Equation (11) above becomes less than 1.00 mm, it is possibleto produce the separator roll 10 (e.g. separator rolls in Examples 1through 8) whose meandering width d is less than 1.00 mm.

n: number of times by which the separator 12 is wound around the core 8

t [μm]: average thickness of the separator 12

φo [mm]: diameter of the core 8

φi [mm]: diameter of the axis hole H

x (0.2 mm): gap length constant

w [mm]: width of the core 8

Furthermore, it is preferable to set the above parameters so that thevalue of Equation (11) is not more than 0.80 mm. This allows for aproduction of the separator roll 10 whose meandering width d is not morethan 0.80 mm.

[Summary]

A separator roll of the present invention is a separator roll,including: a core; and a battery separator wound around the core, thecore having an axis hole along a central axis of the core, a value beingnot less than 0.3 and not more than 1.5, the value being obtained bydividing, by a width of the core in a direction of the central axis, adifference between a diameter of the core and a diameter of the axishole.

The inventors of the present invention have found that when a valueobtained by dividing a difference between a diameter of the core and adiameter of the axis hole by a width of the core in a direction of thecentral axis is within a specific range smaller than that of aconventional core, it is possible to greatly reduce a width by which thebattery separator meanders (hereinafter “meandering width”). With theabove arrangement, it is possible to reduce a meandering width ascompared with a conventional separator roll.

The separator roll of the present invention may be arranged such thatthe core has a diameter of less than 125 mm, and a diameter ratio,obtained by dividing the diameter of the core by the diameter of theaxis hole, is not less than 1.25 and not more than 1.65.

A separator roll of the present invention is a separator roll,including: a core; and a battery separator wound around the core, thecore having an axis hole along a central axis of the core, the corehaving a diameter of less than 125 mm, a diameter ratio, obtained bydividing the diameter of the core by a diameter of the axis hole, beingnot less than 1.25 and not more than 1.65.

The inventors of the present invention have found that when a diameterratio obtained by dividing a diameter of the core by a diameter of theaxis hole is within a specific range smaller than that of a conventionalcore, it is possible to greatly reduce a meandering width. With theabove arrangement, it is possible to reduce a meandering width ascompared with a conventional separator roll.

The separator roll of the present invention may be arranged such that avalue, obtained by dividing a diameter of the separator roll by thediameter of the axis hole of the core, is not less than 2.3 and not morethan 3.5.

The inventors of the present invention have found that when a valueobtained by dividing a diameter of the separator roll by a diameter ofthe axis hole of the core is within a specific range, it is possible toreduce a load on a surface-protruding mechanism which applies a certainfrictional force to the core and transmits to the core a rotating forceof a take-up roller that is rotating. With the above arrangement, theload on the surface-protruding mechanism can be reduced, so thatdeformation or deterioration of the core can be prevented. Thisstabilizes winding up and winding off of the separator, thereby furtherreducing a meandering width as compared with a conventional separatorroll.

The separator roll of the present invention may be arranged such thatthe core includes: an outer cylinder part, an inner cylinder partprovided inside the outer cylinder part, the inner cylinder partsurrounding the axis hole extending along the central axis of the core,and a plurality of support members provided, at intervals, between theouter cylinder part and the inner cylinder part so as to support them,the plurality of support members each having a length of 5 mm or more ina radial direction of the core.

With the arrangement, the core has gaps each surrounded by the outercylinder part, the inner cylinder part, and the support members. The gaphas a length of 5 mm or more in a radial direction of the core.Consequently, by inserting a part of a conveyer, human's finger etc.into the gap(s), it is possible to easily convey the separator roll.

A method of the present invention of producing a separator roll is amethod of producing a separator roll, the separator roll including acore and a battery separator wound around the core, the core having anaxis hole along a central axis of the core, a value being not less than0.3 and not more than 1.5, the value being obtained by dividing, by awidth of the core in a direction of the central axis, a differencebetween a diameter of the core and a diameter of the axis hole, themethod comprising the steps of: inserting a take-up roller into the axishole and fixing the core to the take-up roller; and winding the batteryseparator around the core while rotating the core along with the take-uproller.

With the method, it is possible to produce a separator roll whosemeandering width is smaller than that of a conventional separator roll.

A method of the present invention of producing a separator roll is amethod of producing a separator roll, the separator roll including acore and a battery separator wound around the core, the core having anaxis hole along a central axis of the core, the core having a diameterof less than 125 mm, a diameter ratio, obtained by dividing the diameterof the core by a diameter of the axis hole, being not less than 1.25 andnot more than 1.65, the method comprising the steps of: inserting atake-up roller into the axis hole and fixing the core to the take-uproller; and winding the battery separator around the core while rotatingthe core along with the take-up roller.

With the method, it is possible to produce a separator roll whosemeandering width is smaller than that of a conventional separator roll.

A method of the present invention of producing a separator roll is amethod of producing a separator roll, the separator roll including acore and a battery separator wound around the core, the core having anaxis hole along a central axis of the core, the method comprising thesteps of: inserting a take-up roller into the axis hole and fixing thecore to the take-up roller; and winding the battery separator around thecore while rotating the core along with the take-up roller, a lengthrepresented by Formula [1] below being less than 1.00 mm.

(2nt+φo)tan(cos⁻¹((φi−x)/(w ² +φi ²)^(1/2))−cos⁻¹(φi/(w ² +φi²)^(1/2)))  [1]

where

n is the number of times by which the battery separator is wound aroundthe core,

t is an average thickness of the battery separator [μm],

φo is a diameter of the core [mm],

φi is a diameter of the axis hole [mm],

x is 0.2 mm, and

w is a width of the core in a direction of the central axis [mm].

With the arrangement, the value represented by the Formula [1] indicatesa meandering width. Thus, it is possible to produce a separator rollwhose meandering width is smaller than that of a conventional separatorroll.

The method of the present invention may be arranged such that the lengthrepresented by the Formula [1] is not more than 0.80 mm.

With the method, it is possible to produce a separator roll whosemeandering width is further smaller than that of a conventionalseparator roll.

[Additional Matter]

The present invention is not limited to the embodiments, but can bealtered by a skilled person in the art within the scope of the claims.An embodiment derived from a proper combination of technical means eachdisclosed in a different embodiment is also encompassed in the technicalscope of the present invention.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a battery separator and a methodof producing the battery separator and to a film other than a batteryseparator and a method of producing the film.

REFERENCE SIGNS LIST

-   8, u, l Core-   10 Separator roll-   70U, 70L, R Take-up roller-   81 Outer cylinder part-   81 a Outer circumferential surface-   82 Inner cylinder part-   83 Rib (support member)-   130 Adhesive tape (fixing tape)-   CA Central axis-   H Axis hole-   n number of times of windings-   φo Diameter of core-   φi Diameter of axis hole of core

1. A separator roll, comprising: a core; and a battery separator woundaround the core, the core having an axis hole along a central axis ofthe core, a value being not less than 0.3 and not more than 1.5, thevalue being obtained by dividing, by a width of the core in a directionof the central axis, a difference between a diameter of the core and adiameter of the axis hole.
 2. The separator roll as set forth in claim1, wherein the core has a diameter of less than 125 mm, and a diameterratio, obtained by dividing the diameter of the core by the diameter ofthe axis hole, is not less than 1.25 and not more than 1.65.
 3. Aseparator roll, comprising: a core; and a battery separator wound aroundthe core, the core having an axis hole along a central axis of the core,the core having a diameter of less than 125 mm, a diameter ratio,obtained by dividing the diameter of the core by a diameter of the axishole, being not less than 1.25 and not more than 1.65.
 4. The separatorroll as set forth in claim 1, wherein a value, obtained by dividing adiameter of the separator roll by the diameter of the axis hole of thecore, is not less than 2.3 and not more than 3.5.
 5. The separator rollas set forth in claim 1, wherein the core includes: an outer cylinderpart, an inner cylinder part provided inside the outer cylinder part,the inner cylinder part surrounding the axis hole extending along thecentral axis of the core, and a plurality of support members provided,at intervals, between the outer cylinder part and the inner cylinderpart so as to support them, the plurality of support members each havinga length of 5 mm or more in a radial direction of the core.
 6. A methodof producing a separator roll, the separator roll including a core and abattery separator wound around the core, the core having an axis holealong a central axis of the core, a value being not less than 0.3 andnot more than 1.5, the value being obtained by dividing, by a width ofthe core in a direction of the central axis, a difference between adiameter of the core and a diameter of the axis hole, the methodcomprising the steps of: inserting a take-up roller into the axis holeand fixing the core to the take-up roller; and winding the batteryseparator around the core while rotating the core along with the take-uproller.
 7. A method of producing a separator roll, the separator rollincluding a core and a battery separator wound around the core, the corehaving an axis hole along a central axis of the core, the core having adiameter of less than 125 mm, a diameter ratio, obtained by dividing thediameter of the core by a diameter of the axis hole, being not less than1.25 and not more than 1.65, the method comprising the steps of:inserting a take-up roller into the axis hole and fixing the core to thetake-up roller; and winding the battery separator around the core whilerotating the core along with the take-up roller.
 8. A method ofproducing a separator roll, the separator roll including a core and abattery separator wound around the core, the core having an axis holealong a central axis of the core, the method comprising the steps of:inserting a take-up roller into the axis hole and fixing the core to thetake-up roller; and winding the battery separator around the core whilerotating the core along with the take-up roller, a length represented byFormula [1] below being less than 1.00 mm.(2nt+φo)tan(cos⁻¹((φi−x)/(w ² +φi ²)^(1/2))−cos⁻¹(φi/(w ² +φi²)^(1/2)))  [1] where n is the number of times by which the batteryseparator is wound around the core, t is an average thickness of thebattery separator [μm], φo is a diameter of the core [mm], φi is adiameter of the axis hole [mm], x is 0.2 mm, and w is a width of thecore in a direction of the central axis [mm].
 9. The method as set forthin claim 8, wherein the length represented by the Formula [1] is notmore than 0.80 mm.